Dimethyl sulfoxide additive to Na2SO4-based polymer electrolytes for low temperature capacitive devices

High Output Voltage Aqueous Supercapacitors by Water Deactivated Electrolyte over Wide Temperature Range

Confined by factors such as low operating voltage, poor temperature resistance, and instability at high voltage, the energy density of conventional symmetric aqueous supercapacitors is undesirable over a wide temperature range. It is still challenging to develop aqueous flexible supercapacitors (AFSCs) that can provide stable and high voltage output (>2.0 V) at extreme ambient temperatures. Here, a strategy for constructing AFSC with ultrahigh output voltages over a wide temperature range is proposed through the development of organohydrogel electrolytes (OHEs) with excellent water deactivation, which achieve a notable output voltage of 3.0 V, and unprecedented energy densities of 23.16 µWh cm-2 at -40 °C (beyond 25 °C), surpassing the performance of all previously reported symmetric supercapacitors with aqueous electrolytes. Theoretical calculations and experimental analyses show that OHEs can deactivate water to increase the output voltage limit of AFSCs by enhancing intermolecular interactions and regulating inter Helmholtz plane. Meanwhile, it also shows excellent flexibility and cycling stability (80.5% after 20 000 cycles at 25 °C and 97.0% after 50 000 cycles at -40 °C). More importantly, OHEs enable AFSCs switchable output voltages (from 2.5 to 3.0 V), making it possible to operate supercapacitors with high energy density and stability at low temperatures.

Dimethyl sulfoxide as a function additive on halogen-free electrolyte for magnesium battery application

Practical Mg batteries still face significant challenges in their development, like the lack of simple compatible electrolytes, self-discharge, the rapid passivation of the Mg anode, and the slow conversion reaction pathway. Here, we propose a simple halogen-free electrolyte (HFE) based on magnesium nitrate (Mg(NO3)2), magnesium triflate Mg(CF3SO3)2, and succinonitrile (SN) dissolved in acetonitrile (ACN)/tetraethylene glycol dimethyl ether (G4) cosolvents, with dimethyl sulfoxide as a functional additive. The addition of DMSO to the HFE changes the interfacial structure at the magnesium anode surface and facilitates the transport of magnesium ions. The as-prepared electrolyte shows high conductivity (σ b = 4.48 × 10-5, 6.52 × 10-5 and 9.41 × 10-5 S cm-1 at 303, 323, and 343 K, respectively) and a high ionic transference number (tmg +2 = 0.91/0.94 at room temperature/55 °C) for the matrix containing 0.75 ml of DMSO. Also, the cell with 0.75 ml of DMSO shows high oxidation stability, a very low overpotential, and steady Mg stripping/plating up to 100 h. Postmortem analysis of pristine Mg and Mg anodes extracted from disassembled Mg/HFE/Mg and Mg/HFE_0.75 ml DMSO/Mg cells after stripping/plating reveals the role of DMSO in improving Mg-ion passage through HFE by evolving the anode/electrolyte interface at the Mg surface. Further optimization of this electrolyte is expected to achieve excellent performance and good cycle stability when applied to the magnesium battery in future work.

Enzymatic Hydrolysis Lignin-Derived Porous Carbons through Ammonia Activation: Activation Mechanism and Charge Storage Mechanism

The low energy density and low cost performance of electrochemical capacitors (ECs) are the principal factors that limit the wide applications of ECs. In this work, we used enzymatic hydrolysis lignin as the carbon source and an ammonia activation methodology to prepare nitrogen-doped lignin-derived porous carbon (NLPC) electrode materials with high specific surface areas. We elucidated the free radical mechanism of ammonia activation and the relationship between nitrogen doping configurations, doping levels, and preparation temperatures. Furthermore, we assembled NLPC∥NLPC symmetric ECs and NLPC∥Zn asymmetric ECs using aqueous sulfate electrolytes. Compared with the ECs using KOH aqueous electrolyte, the energy densities of NLPC∥NLPC and NLPC∥Zn ECs were significantly improved. The divergence of charge storage characteristics in KOH, Na₂SO₄, and ZnSO₄ electrolytes were compared by analyzing their area surface capacitance. This work provides a strategy for the sustainable preparation of lignin-derived porous carbons toward ECs with high energy densities.